Electric heating element



Sept. 20, 1938. M. M. J. COUPIER 2,130,715

ELECTRIC HEATING ELEMENT Filed July 9, 1955 men 72) r.-

V ZJTEQ JM" Patented Sept. 20, 1938 I ELECTRIC HEATING ELEMENT Marcel Marie Joseph Eugene Coupier, Paris,

France Application July 9, 1935, Serial No. 30,578, In France July 19, 1934 3 Claims. (Cl. 201-457) It is well known that electric heating elements scribed hereinafter by way of example, without may comprise a resistant helically wound wire this description being in any manner limitative.

embedded in mineral insulating material such as In the case of rectilinear elements, I may use magnesia, the whole being enclosed in an outer a sufliciently hard metallic core constituting a 5 metal sheath. mandrel which is removed after compression of 5 The mineral insulation may be introduced as a the insulating material, which removal may be powder inside a metallic tube containing a helfurthered by a conical shape given to the mandrel ically wound resistance, after which said tube is or by a he groove thereon which allows the closed at its ends and is submitted to an outer removal of the mandrel through rotation, said compression through tensioning or restriction of helical groove being associated. if required with iii area, so as to provide a good thermic contact and a conical shape of the mandrel. sufiicient compactness. In the same-case of rectilinear elements, 1 may On the other hand the insulating material, also use a central core, threaded or not, of inconstituted say by magnesia, may be formed in sulating material, moulded or machined and situ starting from magnesium in which case the capable of retaining its electric properties at the coiled resistance is held in place by reason of the temperature of use. It is sufficient for the maswelling of the magnesia when forming. terial of the core to show at the start a resistance The first method mentioned does not allow a to deformation such that it may resist the final perfect contact to be obtained as the possible compression to which the insulation embedding compression may be limited by the fact that when the resistant coil is to be submitted. I may use Be it is attempted to increase it, there is a risk of for instance small rods of compressed steatite or breaking the coiled resistance. The second special porcelain or even metallic cores enclosed method which provides a better contact shows in sheaths of mica or the like hard insulating the drawback that it forms a limitation to the material. In the case of a core formed of a cenchoice of the insulating material, and furthertral metal part enclosed in an insulating sheath 25 more that it requires a passage through the meof insulating material such as compressed powtallic stage, whereas it may be of interest to use der, the central metal part or core 1n a y be redirectly pulverized mineral material which may moved or not after compression. a be set in place either directly or as compressed When the resistances are to be folded after they tablets of insulating material to be crushed have been embedded in compressed insulating so through compression, once in place. material, I may use for the inner core insulating My invention has for its object a method for material capable of being folded when hot or cold making electric heating elements providing the 'without any damage to the resistant wire. Thus advantages of the first abovedescribed method for instance the core may be constituted, in the without showing its drawbacks. It consists in part to be bent alone or throughout, by a mandrel 35 using when compressing the pulverized insulating capable of deformation when hot or cold adapted material, a solid core holding inwardly the resistto be removed or left in place according as to ance coil so as to avoid the crushing of the latter whether it is electrically conductive or becomes and to provide a more considerable compression so for instance when hot or is not conductive.

40 of the insulation than with the methods used j I may for instance use a mandrel of insulat- 40 heretofore. ing material such as agglomerated mica and glass The insulation may be simply'in the pulverized which softens when very hot and thus allows state, or form tablets of compressed powder. the bending of the hot core, while holding the As to the solid core; it may be of insulating or resistant winding which remains properly cenconducting material. Thus it may be of a pultered inside its sheath of compact powder. 45 verable compressed material similar to or diifer- I may also in certain cases use a metal or ent' from the pulverized insulating material, of alloy which melts sufllciently underneath the material-softening when hot, or fusible or friable melting point of the resistance and of its sheath or of any desired metal. for preventing any alloying therewith and al- 60 h According to its nature or according to the delowing it to flow out so as to leave the central formations to be imparted to the heating resistpart of the finished resistance free after comant element after compression of the insulating pression, I may in particular use to this end, material, the core may be left in place after said aluminium alloys which allow-an oxidation of any compression or be removed. traces of metal remaining after, melting so as 86 Diflerentpossible forms for execution are deto transform them into insulating particles. It

comprises a cylindrical mandrel i of aluminium or an alloy thereof or of other convenient material. On said mandrel is wound a conducting wire 2 constituting the heating resistance; the

mandrel and wire are disposed inside a metallic sheathing 3 and the hollow. space remaining between the mandrel and sheathing is filled with mineral powdered material, say with magnesia. The-sheathing is closed at both ends by convenient plugs to prevent the magnesia from falling out; the assembly thus prepared is then submitted to a pressure (rolling or drawing). After said operation the assembly may eventually be bent hot or cold, and then submitted to a temperature such that the mandrel melts and flows out without damaging the wire.

The core may also be constituted by insulating material of the same nature as or of a nature difierent from the insulating material surrounding the conducting coil. This core, being thus made of compressed powder will, when'the resistant element is deformed, be reduced into powder without any modification in volume. It continues therefore filling without any lack of continuity the inside of the element. The core may in particular be constituted by small cylindrical rods of very grea ly compressed magnesia.

This core may as stat d hereinabove, be compound and comprise an inner part of metal enclosed inside a system of cylindrical rods of compressed insulating material which maintains the insulation between the winding and the core during bending when the metal has not been previously removed.

The heating element may be made by winding the winding over the core or else by engaging the core inside the winding and causing the coils to bear against the core through a. traction exerted on the ends of the winding while it is engaged inside the outer sheath and the insulation is compressed round it.

When the outer insulating material is formed of compressed tablets or blocks, I prefer giving the core a rate of compression which is higher than that of the compression exerted on the outer insulating material.

The core may also be constituted by a highly tempered glass rod. Such a core is sumciently resistant to allow a tight winding round it of the resistant wire and will resist the compression without breaking but it will crumble into fine granular particles, which cannot damage the wire, when the final shape is being given to the resistant element.

I may of course introduce insulating powder in any suitable manner round the winding and in fact in the case of magnesia insulation prepared in situ I may compress it after formation over a removable or stationary core so as to improve its compactness.

In the case where the core, set in place during compression, is subsequently removed, it is possible to submit the element constituted by the external tube or sheath, the compressed mineral insulation and the winding inside which a vacant space remains, to any of the usual treatments rendering the insulating material less hygroscopic or more compact such as for in stance an impregnation with boric acid.

I have only mentioned hereinabove the application of my invention to heating elements; but obviously it applies also and still better to conducting windings and solenoids for which the setting in place and winding over a core are rendered more easy by the larger size of the coils.

What I claim is:

l. A method for making an electric resistance which comprises winding a conductor as a helix over a core of aluminium, embedding said core and conductors in a mineral insulation material, enclosing said embedded core and conductor within a metal sheath, subjecting said sheath and its content to the action of pressure, bending the whole to a desired shape and then submitting it to the action of a temperature above the melting point of the core, whereby the melted core runs out of the sheath.

2. A method i'or'making a substantially cylindrical electric resistance which comprises winding a conductor as a helix over a core of aluminium, embedding said core and conductor in a mineral insulation material, enclosing said embedded core and conductor within a metal sheath, subjecting said sheath and its contents to the action of pressure, and then submitting it to the action of a temperature above the melting point of the core, whereby the melted core runs out of the sheath.

3. A method for making a curved electric resistance which comprises winding a conductor as a helix over a core of aluminium, embedding said core and conductor in a mineral insulation material, enclosing said embedded core and conductor within a metal sheath, subjecting said sheath and its contents to the action of pressure, bending the sheath and its contents to the desired shape, heating said sheath and contents sufiiciently to melt the aluminium core, and allowing said melted core to run 011.

MARCEL'MARIEJOSEPH EUGENE COUPIER. 

